Stockholders' Equity and Stock-based Compensation Expense - Activity Of Options Outstanding Under the 2019 Plans (Details) - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Shares Available for Grant
Beginning balance (in shares)	1,085,170
Additional shares reserved (in shares)	450,000
Options granted (in shares)	(172,139)
Stock awards canceled (in shares)	295,392
Options canceled / forfeited / expired (in shares)	(24,090)
Ending balance (in shares)	1,005,398	1,085,170
Number of Stock Options Outstanding
Beginning balance (in shares)	217,007
Options granted (in shares)	172,139
Options exercised (in shares)	(57,498)
Options canceled / forfeited / expired (in shares)	(24,090)
Ending balance (in shares)	307,558	217,007
Weighted- Average Exercise Price
Beginning balance (in dollars per share)	$ 22.35
Granted (in dollars per share)	30.71
Options exercised (in dollars per share)	24.49
Options canceled / forfeited / expired (in dollars per share)	32.90
Ending balance (in dollars per share)	$ 25.80	$ 22.35
Weighted Average Remaining Term (in Years)
Weighted average remaining term (in years)	4 years 10 months 2 days	3 years 9 months
RSUs
Shares Available for Grant
Awards granted (in shares)	(213,522)
PSUs
Shares Available for Grant
Awards granted (in shares)	(463,593)